R.A.S.C.A.L. Unit in Columbus OH.  They also serve central and southern Ohio through their mobile units.

Lovethatcat.com - Low cost or free s/n programs in U.S.

USA & Worldwide Low Cost or Free Spay  Neuter Resource List Organized by Location & Area Code.

Shelters, Rescues, SpayNeuter by state

American Partnership for Pets

Animal Protection Institute - Spaying and Neutering

ASPCA: NYC Resources: ASPCA Cares

AWARE - Spay & Neuter - ESP - Early Sterilization Program

Best Friends - 9 model spay/neuter programs (pdf)

Bugsy's Animal Network - Help to Stop Pet Over Population!

Collier Spay Neuter Clinic (non profit) located in Naples Florida

Diabella's

The Dog Hause: Spay/Neuter T-Shirts

Early-Age Neutering: Instructional Video for Veterinarians

FCC Feral Cat Fix-athon

Friends of Animals -  Spay Neuter Program

IARL - MODEL MANDATORY SPAY/NEUTER STATUTE

Maddie's Fund - No-Kill Movement

NeuterNeuterLand

NHSPCA: Guide to financial assistance for spaying and neutering

No Puppy Mills Canada - Should I Spay or Neuter my Pet?

PaLC: Animal Friendly License Plates Availability

Pawprints and Purrs - Don't Litter - Spay and Neuter

PAWS: Edmonds Spay Neuter Initiative

PETA - FixCats.com: Be responsible. Spay or neuter your cat.

PETA - Model Spay and Neuter Ordinances

ThePetCenter.com - Spay and Neuter Surgery Photos

The Pet Overpopulation Library

S.N.Y.P. Spay Neuter Your Pet

Spay Day USA - Doris Day Animal Foundation

Spay Neuter Incentive Project (SNIP)

SPAY/USA

University of Illinois - Early Spay/Neuter: An Overview

US and Canada Spay/Neuter Resources

The Winn Feline Foundation - Report

http://www.lovethatcat.com/spayneuter.html - Low Cost or Free Spay - Neuter Programs in the U.S..

Low Cost or Free Spay/Neuter Programs in the U.S

http://www.savesamoa.org/html/spay_neuter.html - Spay and Neuter Resources.

http://www.wbko.com/news/headlines/214841.html - Spay and Neuter Awareness Month.

SPAY/USA: A program of The Pet Savers Foundation, is a nationwide network and referral service for affordable spay/neuter services.

http://www.pbrc.net/speuter.html ~ Low Cost/Free Spay/ Neuter Programs

Metroplex Animal Coalition.